Paramyotonia congenita (PMC) is characterized by nondystrophic myotonia aggravated by exercise and cold exposure. SCN4A mutations manifest as various phenotypes of channelopathy, including PMC, myotonia congenita, and periodic paralysis. SCN4A-related channelopathy is characterized by autosomal dominant inheritance. Parental gonadal mosaicism is suspected in cases of recurrent de novo mutation in an autosomal dominantly inherited disease. We report a case of two Korean brothers presenting with PMC due to same de novo SCN4A point mutation, probably due to parental gonadal mosaicism.

Colchicine is widely used in the treatment of gouty arthritis, and chronic use of colchicine can cause vacuolar myopathy. We report colchicine-induced myopathy with electrophysiological myotonia in a patient with gouty arthritis. A 86-year-old man with gouty arthritis presented with progressive proximal weakness and gait disturbance. Electrophysiological finding showed myotonic myopathy and muscle biopsy revealed a vacuolar myopathy. His symptoms soon resolved with the discontinuation of colchicine.